Functional response curves of avian molluscivores: high intake rates maintained even at low prey density

摘要

Despite its low energy density, the blue mussel Mytilus edulis is a regular prey of various seaduck species. As a result, seaducks must ingest large quantities of mussels to meet their energy requirements. In this study, we modeled the functional response curve for a large avian molluscivore, the common eider Somateria mollissima, by measuring intake rates of captive individuals foraging in diving tanks under different mussel densities and at different attachment strengths. We estimated the mean maximum intake rate to be 45 prey min(-1) (with a mean bottom time +/- SD of 5.034 +/- 3.793 s), which is relatively high compared to intake rates of other diving duck species and prey types. However, we found no significant effects of density and attachment strength on intake rates, indicating that eiders can maintain maximum intake rates even at low mussel densities. These results could explain the depletion of mussel beds sometimes observed in the wild, as well as the large negative impact that seaducks may have in aquaculture farms.